Fuel Pressure for Quadrajet?

[cleszkie]

I have been experiemnting for a while now to find the best fuel pressure for my Q-jet. Want to see what has worked for others. I find that I'm between 5 and 7 psi. However, within this range, I find that my idle RPM will change. Idle RPM will increase slightly with higher fuel pressure, and decrease slightly with lower fuel pressure. Why is that?

[RED 1970]

I don't know about q-jets but sounds like the extra fuel pressure might be pushing a little extra fuel past the needle/seat.

[CSGAS]

Indeed it is, and you'll find that at the higher pressure you'll have a hard time pinning down an idle mixture because there will be a few screw turns that seem to make no difference in the way the engine runs.

For the street, my mentor taught me that Q-jets like 4.5-5.5 psi, and I've never seen anything to contradict that personally. Higher pressure should be used for off-road applications, like the strip, mud bogging, or marine tune...it improves performance off the line then, and you don't worry about fuel mixture at idle.

[cleszkie]

RED 1970 & CSGAS - I think you guys are on the money with the high pressure pushing fuel past the needle seat. Just as CSGAS stated, I am having trouble pinning down my idle mixture because I have those idle screw turns that don't affect the idle quality like they should. Thanks for the input.